Ill 



PASTEUR AND HYDROPHOBIA 157 



introducing the modified virus into the body of an 

 animal is due to the education of the living proto- 

 plasmic cells of which the animal consists. If you 

 plunge a mussel from the sea into fresh water, making 

 sure that its shell is kept a little open, the animal will 

 be killed by the fresh water. But if you treat the 

 mussel first with ''modified" fresh water — that is, 

 with brackish water — and then after a bit introduce 

 it to fresh water, the fresh water will have no injurious 

 efi'ect, and the mussel may be made to permanently 

 tolerate fresh water. So too by commencing with 

 small doses, gradually increased, the human body may 

 be made to tolerate an amount of arsenic and of other 

 poisons which are deadly to the uneducated. 



Any one of these three suppositions would at first 

 sight seem to ofi"er a possible explanation of the pro- 

 tective inoculation against rabies and hydrophobia. 

 It is not known that the virus of rabies is a separate 

 parasitic organism ; at the same time it is possible that 

 it is. If it is not, the last of the three above-named 

 hypotheses would seem to meet the case, and, whether 

 the virus is a living thing or not, has an appearance 

 of plausibility. 



But how are we to suppose that the inoculation 

 of modified rabbit's virus acts upon a man so as 

 to cut short the career of a dog's virus which has 

 already been implanted in the man's system by a 

 bite? 



To form any plausible conception on this matter 

 we ought to have some idea as to the real significance 

 of "the incubation period," and this we are not yet 



